The present invention relates to magnetoresistive read sensors for reading signals recorded in a magnetic medium, and more particularly, this invention relates to tailoring a spacer of a spin valve magnetoresistive read sensor for improving operating characteristics.
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR elementxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization of the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material separated by a layer of non-magnetic electrically conductive material are generally referred to as spin valve (SV) sensors manifesting the GMR effect (SV effect). In an spin valve sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO, FeMn, PtMn) layer. The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In spin valve sensors, the spin valve effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium causes a change in the direction of magnetization in the free layer, which in turn causes a change in resistance of the spin valve sensor and a corresponding change in the sensed current or voltage. It should be noted that the AMR effect is also present in the spin valve sensor free layer.
FIG. 1 shows a typical spin valve sensor 100 (not drawn to scale) comprising end regions 104 and 106 separated by a central region 102. The central region 102 has defined edges and the end regions are contiguous with and abut the edges of the central region. A free layer (free ferromagnetic layer) 110 is separated from a pinned layer (pinned ferromagnetic layer) 120 by a non-magnetic, electrically-conducting spacer 115.
The spacer layer 115 separating magnetic free layer 110 and pinned layer 120 is critical for the performance of any type of spin valve device. Variety of spacer materials have been evaluated in the past, and copper (Cu) is commonly accepted as leading to the best spin valve characteristics, and is commonly used in device applications.
The magnetization of the pinned layer 120 is fixed through exchange coupling with an antiferromagnetic (AFM) layer 125. Free layer 110, spacer 115, pinned layer 120 and the AFM layer 125 are all formed in the central region 102. Hard bias layers 130 and 135 formed in the end regions 104 and 106, respectively, provide longitudinal bias for the free layer 110. Leads 140 and 145 formed over hard bias layers 130 and 135, respectively, provide electrical connections for the flow of the sensing current Is from a current source 160 to the MR sensor 100. Sensor 170 is connected to leads 140 and 145 senses the change in the resistance due to changes induced in the free layer 110 by the external magnetic field (e.g., field generated by a data bit stored on a disk). IBM""s U.S. Pat. No. 5,206,590 granted to Dieny et al. and incorporated herein by reference, discloses an MR sensor operating on the basis of the spin valve effect.
Another type of spin valve sensor is an anti-parallel (AP)-pinned spin valve sensor. FIG. 2A shows an exemplary AP-Pinned spin valve sensor 200 (not drawn to scale). Spin valve sensor 200 has end regions 202 and 204 separated from each other by a central region 206. AP-pinned spin valve sensor 200 comprises a Ni-Fe free layer 225 separated from a laminated AP-pinned layer 210 by a copper spacer layer 220. The magnetization of the laminated AP-pinned layer 210 is fixed by an AFM layer 208, or pinning layer, which is made of NiO. The laminated AP-pinned layer 210 includes a first ferromagnetic layer 212 (PF1) of cobalt and a second ferromagnetic layer 216 (PF2) of cobalt separated from each other by a ruthenium (Ru) anti-parallel coupling layer 214. The AMF layer 208, AP-pinned layer 210, copper spacer 220, free layer 225 and a cap layer 230 are all formed sequentially in the central region 206. Hard bias layers 235 and 240, formed in end regions 202 and 204, provides longitudinal biasing for the free layer 225. Electrical leads 245 and 250 are also formed in end regions 202 and 204, respectively, to provide electrical current from a current source (not shown) to the spin valve sensor 200.
Various parameters of a spin valve sensor may be used to evaluate the performance thereof. For example, the structure sheet resistance (R), GMR ratio (xcex94R/R), and ferromagnetic interlayer coupling field (Hf) are all performance indicators.
R and xcex94R/R
Spin valve effects are characterized by xcex94R/R, which is defined as (RAPxe2x88x92Rp)/Rp, where RAP is the anti-parallel resistance and Rpis the parallel resistance.
Numerous theoretical studies have attempted to explain the behavior of spin valve effects. However, there does not currently exist an explanation of the main factors controlling the magnitude of the sensor response, as characterized by xcex94R/R, as it relates to the required properties of the conductive spacers and ferromagnetic (FM) layers constituting such device. Experimental efforts have been largely based on trial and error, by investigating various combinations of FM layers and conductive spacer layers. None of the previous work has yielded quantitative guidelines for the maximization of xcex94R/R for spin valve sensors by providing selection criteria for the layer compositions of the FM material and the conductive spacer.
What is known is that the GMR effect depends on the angle between the magnetizations of the free and pinned layers. More specifically, the GMR effect is proportional to the cosine of the angle B between the magnetization vector of the pinned layer (Mp) and the magnetization vector of the free layer (MF) (Note FIGS. 2B and 2C). In a spin valve sensor, the electron scattering and therefore the resistance is maximum when the magnetizations of the pinned and free layers are antiparallel, i.e., majority of the electrons are scattered as they try to cross the boundary between the MR layers. On the other hand, electron scattering and therefore the resistance is minimum when the magnetizations of the pinned and free layers are parallel; i.e., majority of electrons are not scattered as they try to cross the boundary between the MR layers.
In other words, there is a net change in resistance of a spin valve sensor between parallel and antiparallel magnetization orientations of the pinned and free layers. The GMR effect, i.e., the net change in resistance, exhibited by a typical prior art spin valve sensor is about 6% to 8%.
During the design of a spin valve sensor, the thickness of the spacer layer is traditionally chosen to be less than the mean free path of conduction electrons through the spin valve sensor. With this arrangement, a portion of the conduction electrons are scattered by the interfaces of the spacer layer with the pinned and free layers. As mentioned earlier, changes in the scattering of the conduction electrons change the resistance of the spin valve sensor in proportion to cos xcex8, where xcex8 is the angle between the magnetizations of the pinned and free layers.
Hƒ
Because of a magnetic coupling between the free and pinned layers, there is an interlayer coupling field Hf between the free and pinned layers. Since the spacer layer of a spin valve sensor affects the magnetic coupling between the free and pinned layers, it also affects Hf and can thus be modified to minimize the same.
There is therefore a need for an improved spacer in a spin valve sensor that alters R, xcex94R/R, and Hf for overall improved performance.
It is an object of the present invention to disclose an improved spin valve sensor that alters R and xcex94R/R for overall improved performance.
It is another object of the present invention to disclose an improved spin valve sensor that alters Hf for overall improved performance.
It is yet another object of the present invention to disclose an improved spin valve sensor with a spacer layer comprising CuOx.
It is still yet another object of the present invention to disclose a method of fabricating an improved spin valve sensor with a spacer layer comprising CuOx.
These and other objects and advantages are attained in accordance with the principles of the present invention by disclosing a spin valve sensor system and method for fabricating the same. Included is a free layer and a pinned layer with a spacer layer disposed between the free layer and the pinned layer. Such spacer layer is oxidized for improving operational characteristics of the spin valve sensor.
In one embodiment of the present invention, the spacer layer may include CuOx. Further, the characteristics that are improved by the oxidation may include R, xcex94R/R, and/or Hf.
In another embodiment of the present invention, the spacer layer may be constructed utilizing physical vapor deposition (PVD) sputtering. Moreover, the spacer layer may be oxidized utilizing in-situ post-oxidation, reactive sputtering in oxygen, or a combination thereof. In the case of in-situ post-oxidation, the spacer layer may be oxidized in an environment characterized between 1E-4 and 1E-2 Torr*min. In the case of reactive sputtering, the spacer layer may be oxidized in an environment characterized between 5xc3x9710xe2x88x928 and 5xc3x9710xe2x88x927 Torr.
In any case, the spacer layer may be oxidized during and/or after being constructed. Further, the spacer layer may comprise a plurality of oxidized sub-layers. It should be noted that the spin valve sensor may take any form such as a top spin valve, a bottom spin valve, a dual spin valve, and/or an anti-parallel (AP)-pinned spin valve sensor.
In another aspect of the present invention, a method may be provided for fabricating the spin valve sensor. During such method for a bottom spin valve, a pinned layer is deposited, and a spacer layer deposited on the pinned layer. Further, a free layer is deposited on the spacer layer. As set forth earlier, the spacer layer is oxidized for improving operational characteristics of the spin valve sensor.